Solid state synthesis of lithium meta arsenate

ABSTRACT

The present invention provides a novel solid state method for the synthesis of lithium meta arsenate (LiAsO 2 ) by mixing a lithium source with arsenious trioxide under controlled conditions to obtain the lithium meta arsenate.

FIELD OF THE INVENTION

[0001] The present invention provides a novel process for the preparation of lithium meta arsenate (LiAsO₂) useful as an intermediate for the preparation of lithium hexafluro arsenate (LiAsF₆) which is a secondary lithium ion battery electrolyte for nonaqueous solid state and polymer electrolyte.

BACKGROUND OF THE INVENTION

[0002] Lithium meta arsenate (LiAsO₂) is not well documented in literature although the corresponding equivalent sodium compound known as sodium meta arsenate (NaAsO₂) is well documented in literature. This compound easily decomposes in acid media to arseneous trioxide (As₂O₃). Since other methods are not available to prepare this compound, as of today there is nothing to write about the disadvantages.

OBJECTS OF THE INVENTION

[0003] The main object of this invention is to provide a novel hitherto unattempted method for the synthesis of lithium meta arsenate (LiAsO₂) salt.

[0004] Another object of this invention is to provide a simple thermal method for the synthesis of lithium meta arsenate (LiAsO₂).

[0005] Yet another object of this invention is to get a pure product from solid state reactions without any side or partial reaction.

[0006] Still yet another object of this invention is to synthesis lithium meta arsenate (LiAsO₂) by thermal method.

[0007] Yet another object of this invention is to provide a clean reaction by mixing equimolar proportions of lithium salts and arsenous trioxide under closed controlled conditions.

SUMMARY OF THE INVENTION

[0008] Accordingly, the present invention provides a novel method for the preparation of lithium meta arsenate (LiAsO₂) comprising mixing a lithium source selected from the group consisting of lithium carbonate (dry and AR), lithium oxide (dry and AR quality), lithium nitrate (dry and AR), lithium hydroxide (dry and AR) and any mixture thereof with arsenious trioxide (dry and AR), grinding the mixture and heating the ground mixture to obtain lithium meta arsenate (LiAsO₂) and cooling the product so obtained.

[0009] In one embodiment of the invention, the reactions are conducted in solid state with the lithium source and arsenious trioxide both being taken in the form of solids.

[0010] In another embodiment of the invention, the lithium source is selected from the group consisting of lithium oxide (dry and AR quality), lithium nitrate (dry and AR) and lithium hydroxide (dry and AR) and the heating of the ground mixture of said lithium source with arsenious trioxide is done at a temperature of 400° C. for 4 hours.

[0011] In another embodiment of the invention, the lithium source comprises lithium carbonate (dry and AR) and the heating of the ground mixture of said lithium source with arsenious trioxide is done at a temperature of 600° C. for 10 hours.

[0012] In another embodiment of the invention, the ground mixture of solid lithium source and solid arsenious trioxide are taken in a silica or porcelain crucible and introduced into a preheated furnace kept at a preheat of 100° C.

[0013] In an embodiment of the invention LiOH or Li₂O or Li₂CO₃ or LiNO₃ is allowed to react with arseneous trioxide (As₂O₃) by a solid state thermal procedure.

[0014] In still another embodiment of the invention the lithium source and the arsenious trioxide are taken in the molar ratio of 1:1 such that lithium: arsenic are in 1:1 proportion. In yet another embodiment of the invention the process is carried out in a single step.

[0015] In yet another embodiment of the invention no side or partial reactions occur.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

[0016]FIG. 1 is the X-ray analysis of the product sample obtained by the process of the invention confirming the purity of the product.

DETAILED DESCRIPTION OF THE INVENTION

[0017] Lithium meta arsenate (LiAsO₂) is prepared in the present invention by the following procedure which can be considered as pure solid state reaction between two solid state material namely lithium salts of lithium hydroxide or lithium oxide or lithium carbonate or lithium nitrate and arsenous trioxide on specific conditions of heating. Hence, lithium meta arsenate (LiAsO₂) is prepared by reacting LiOH or LiNO₃ or Li₂CO₃ or Li₂O with As₂O₃ under controlled heating conditions. A solid state reaction occurs between the salts of lithium mentioned above with arseneous trioixide at specific temperatures and the product lithium meta arsenate (LiAsO₂) is formed. Arsenous trioxide is mixed with equimolar proportions of LiOH or LiNO₃ or Li₂Co₃ or Li₂O salt and the mixture was ground well and the ground mixture was transferred into a silica/porcelain crucible. The crucible containing the lithium salt and arsenous trioxide mixture was slowly heated to 100° C. and then heated to 400° C. for 10 hours in an electric furnace continuously maintaining the temperature. However, in the case of lithium carbonate, arsenous troxide mixture the heating was raised to 600° C. keeping the same time as 10 hours for maintaining the temperature.

[0018] The reaction occurring during the solid state process is given below

2LiX+As₂O₃ - - - →2LiAsO₂+2X where X is OH⁻, O²⁻, NO₃ ⁻, CO₃ ²⁻

[0019] A novel method for the preparation of lithium meta arsenate (LiAsO₂) was developed wherein lithium carbonate (dry and AR) or lithium oxide (dry & AR quality) or lithium nitrate (dry and AR) and lithium hydroxide (dry and AR) are mixed with equimolar quantity or arsenous trioxide (dry and AR). The mixture is ground well and then transferred to a silica or porcelain crucible. The crucible is inserted into a preheated electric furnace kept at a temperature of 100° C. and the heating was slowly raised to 400° C. and the temperature maintained for 4 hours for the mixture containing any of the following lithium salts—LiOH or LiNO₃ or Li₂O salt. For the mixture containing Li₂CO₃ however the temperature was raised to 600° C. and the heating continued for 10 hours. The product was then removed from the furnace after cooling and analysed the sample by X-ray to confirm the purity and identity of the product.

[0020] The reactions that occur are:

[0021] a. 2LiOH+As₂O₃→2LiAsO₂+H₂O

[0022] b. 2LiNO₃+As₂O₃→2LiAsO₂+2NO2

[0023] c. Li₂CO₃+As₂→2LiAsO₂+CO₂

[0024] d. Li₂O+As₂O₃→2LiAsO₂

[0025] LiOH or Li₂O or Li₂CO₃ or LiNO₃ is allowed to react with arseneous trioxide (As₂O₃) by a solid state thermal procedure. The lithium salt and the arsenic salt are taken in the molar ratio of 1:1 such that lithium: arsenic is in 1:1 proportion. A feature of this invention is that the process is carried out in a single step. No side or partial reactions occur.

[0026] The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention.

EXAMPLE 1

[0027] Pure and dry Li₂CO₃ is mixed with pure and dry arsenous oxide in equimolar proportion. The mixture was ground well and then the ground mixture was transferred into a silica/porcelain crucible. The mixture was introduced into an electric furnace kept at 100° C. After keeping the mixture for an hour at 100° C. the temperature of the furnace was elevated to 600° C. The heating was done for 10 hours. The heating was discontinued and the furnace was cooled to room temperature. The product obtained was analyzed. Components Composition Li₂CO₃ 0.74 g As₂O₃ 1.98 g Initial Temperature 100° C. Time 1 hours Final Temperature 600° C. Time 10 hours Colour of the product White Efficiency of the process >92%

EXAMPLE 2

[0028] Pure and dry LiOH is mixed with pure and dry arsenous oxide in equimolar proportions. The mixture was ground well and then the ground mixture was transferred into a silica/porcelain crucible. The mixture was introduced into an electric furnace kept at 100° C. After keeping the mixture for an hour at 100° C. the temperature of the furnace was elevated to 400° C. The heating was done for 10 hours. The heating was discontinued and the furnace was cooled to room temperature. The product obtained was analyzed. Components Composition LiOH 0.84 g As₂O₃ 1.98 g Initial Temperature 100° C. Time 1 hour Final Temperature 400° C. Time 10 hours Colour of the product White Efficiency of the process >95%

EXAMPLE 3

[0029] Pure and dry LiNO₃ is mixed with pure and dry arsenous oxide in equimolar proportions. The mixture was ground well and then the ground mixture was transferred into a silica/porcelain crucible. The mixture was introduced into an electric furnace kept at 100° C. After keeping the mixture for an hour at 100° C. the temperature of the furnace was elevated to 400° C. The heating was done for 10 hours. The heating discontinued and the furnace was cooled to room temperature. The product obtained was analyzed. Components Composition LiNO₃ 2.46 g As₂O₃ 7.5 g Initial Temperature 100° C. Time 1 hour Final Temperature 400° C. Time 10 hours Colour of the product White Efficiency of the process >92%

EXAMPLE 4

[0030] Pure and dry Li₂O is mixed with pure and dry arsenous oxide in equimolar proportions. The mixture was ground well and then the ground mixture was transferred into a silica/porcelain crucible. The mixture was introduced into an electric furnace kept at 100° C. After keeping the mixture for an hour at 100° C. the temperature of the furnace was elevated to 400° C. The heating was done for 10 hours. The heating was discontinued and the furnace was cooled to room temperature. The product obtained was analyzed. Components Composition Li₂O 0.6 g As₂O₃ 1.98 g Initial Temperature 100° C. Time 1 hour Final Temperature 400° C. Time 10 hours Colour of the product White Efficiency of the process >95%

CONCLUSION

[0031] 1. Lithium salts like Li₂O, Li₂CO₃, LiOH, LiNO₃ or the mixtures are used to react with arseneous trioxide in the molar ratio 1:1.

[0032] 2. Lithium salts Li₂O, Li₂CO₃, LiOH, LiNO₃ react with As₂O₃ to form LiAsO ₂.

[0033] 3. A solid state reaction occurs when arseneous trioxide reacts with Li₂O, Li₂CO₃, LiOH, LiNO₃.

[0034] 4. It is a single step procedure. 

We claim:
 1. A method for the preparation of lithium meta arsenate (LiAsO₂) comprising mixing a lithium source selected from the group consisting of lithium carbonate (dry and AR), lithium oxide (dry and AR quality), lithium nitrate (dry and AR), lithium hydroxide (dry and AR) and any mixture thereof with arsenious trioxide (dry and AR), grinding the mixture and heating the ground mixture to obtain lithium meta arsenate (LiAsO₂) and cooling the product so obtained.
 2. A method as claimed in claim 1 wherein the reaction is conducted in solid state with the lithium source and arsenious trioxide both being taken in the form of solids.
 3. A method as claimed in claim 1 wherein the ground mixture of solid lithium source and solid arsenious trioxide are taken in a silica or porcelain crucible and introduced into a preheated furnace.
 4. A method as claimed in claim 1 wherein the furnace is kept at a pre heat of 100° C.
 5. A method as claimed in claim 1 wherein the lithium source is selected from the group consisting of lithium oxide (dry and AR quality), lithium nitrate (dry and AR) and lithium hydroxide (dry and AR) and the heating of the ground mixture of said lithium source with arsenious trioxide is done at a temperature of 400° C. for 4 to 10 hours.
 6. A method as claimed in claim 1 wherein the lithium source comprises lithium carbonate (dry and AR) and the heating of the ground mixture of said lithium source with arsenious trioxide is done at a temperature of 600° C. for 10 hours.
 7. A method as claimed in claim 1 wherein the LiOH or Li₂O or Li₂CO₃ or LiNO₃ is reacted with arseneous trioxide (As₂O₃) by a solid state thermal procedure.
 8. A method as claimed in claim 1 wherein the the lithium source and the arsenious trioxide are taken in the molar ratio of 1:1 such that lithium:arsenic are in 1:1 proportion.
 9. A method as claimed in claim 1 wherein the process is carried out in a single step.
 10. A method as claimed in claim 1 wherein no side or partial reactions occur. 